As publicly known, a cylinder head for an internal combustion engine is provided with an intake port, an exhaust port, and a water jacket located around an ignition plug mounting hole between an upper deck and a lower deck. The cylinder head is cooled by cooling water that flows through the water jacket.
Conventionally, Patent Document 1 proposes a cylinder block configured such that pillar portion, which couples an upper deck with a lower deck, is provided between an ignition plug mounting hole and a plane including two adjacent head bolt through holes. In the cylinder head disclosed in Patent Document 1, the pillar portions are provided so that the stress around each ignition plug is relieved, while ensuring the cooling performance around the ignition plugs.
Patent Document 2 discloses a cylinder head in which head bolt bosses are connected to intake and exhaust ports by a thickened portion provided in a lower deck to increase the rigidity of the lower deck. Patent Document 3 discloses a cylinder head in which ribs that connect upstream openings of exhaust ports with each other are provided on an upper surface of a lower deck to increase the rigidity of the lower deck.